Observation of large-scale traveling ionospheric disturbances by spaced-path high-frequency instantaneous-frequency measurements

Abstract

The instantaneous frequency of WWV 20 Mc/s (Washington, D.C.) and that of a highly stable c-w signal at 18 Mc/s from Puerto Rico have been simultaneously and continuously recorded between October 1960 and September 1961 both at Stanford, California, and at Seattle, Washington. Traveling ionospheric disturbances have been identified by noting similar frequency fluctuations on the four transmission paths that have appropriate time delays and are in the appropriate order. Because of the wide separation of the paths, only large-scale disturbances moving at high speed could be detected. From 1600 hours of data (usually from 1600 to 0200 UT) between October 1960 and April 1961, nine traveling disturbances have been positively recognized. Velocities and spatial lengths are deduced in six of them, assuming that these disturbances travel at a constant speed. Velocities range from 1450 to approximately 2750 km/hr, and spatial lengths from 1300 to more than 2000 km. The direction of travel cannot be determined accurately, but for all it is from north to south. On four occasions sudden frequency changes, correlated with sudden changes in the earth's magnetic field, preceded the appearance of large-scale traveling disturbances. It is suggested that these disturbances may have been launched by the same event that gave rise to the sudden change in the earth's magnetic field.